Python基础算法库Numpy及可视化库使用实践-大数据ML样本集案例实战

栏目: Python · 发布时间: 5年前

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1 Numpy详细使用

  • 读取txt文件

    import numpy
      world_alcohol = numpy.genfromtxt("world_alcohol.txt", delimiter=",")
      print(type(world_alcohol))
    
      world_alcohol = numpy.genfromtxt("world_alcohol.txt", delimiter=",", dtype="U75", skip_header=1)
      print(world_alcohol)
      
      [[u'1986' u'Western Pacific' u'Viet Nam' u'Wine' u'0']
       [u'1986' u'Americas' u'Uruguay' u'Other' u'0.5']
       [u'1985' u'Africa' u"Cte d'Ivoire" u'Wine' u'1.62']
       ..., 
       [u'1987' u'Africa' u'Malawi' u'Other' u'0.75']
       [u'1989' u'Americas' u'Bahamas' u'Wine' u'1.5']
       [u'1985' u'Africa' u'Malawi' u'Spirits' u'0.31']]
    复制代码
  • 创建一维和二维的Array数组

    #The numpy.array() function can take a list or list of lists as input. When we input a list, we get a one-dimensional array as a result:
      
      #一维的Array数组[]
      vector = numpy.array([5, 10, 15, 20])
      
      #二维的Array数组[[],[],[]]
      matrix = numpy.array([[5, 10, 15], [20, 25, 30], [35, 40, 45]])
      print vector
      print matrix
    复制代码
  • shape用法

    #We can use the ndarray.shape property to figure out how many elements are in the array
      vector = numpy.array([1, 2, 3, 4])
      print(vector.shape)
      
      #For matrices, the shape property contains a tuple with 2 elements.
      matrix = numpy.array([[5, 10, 15], [20, 25, 30]])
      print(matrix.shape)
      
      (4,)
      (2, 3)
    复制代码
  • dtype用法(numpy要求numpy.array内部元素结构相同)

    numbers = numpy.array([1, 2, 3, 4])
      numbers.dtype
      
      dtype('int32')
      
      #改变其中一个值时,其他值都会改变
      numbers = numpy.array([1, 2, 3, '4'])
      print(numbers)
      numbers.dtype
      
     
      ['1' '2' '3' '4']
       dtype('<U11')
    复制代码
  • 索引定位

    [[u'1986' u'Western Pacific' u'Viet Nam' u'Wine' u'0']
       [u'1986' u'Americas' u'Uruguay' u'Other' u'0.5']
       [u'1985' u'Africa' u"Cte d'Ivoire" u'Wine' u'1.62']
       ..., 
       [u'1987' u'Africa' u'Malawi' u'Other' u'0.75']
       [u'1989' u'Americas' u'Bahamas' u'Wine' u'1.5']
       [u'1985' u'Africa' u'Malawi' u'Spirits' u'0.31']]
       
      uruguay_other_1986 = world_alcohol[1,4]
      third_country = world_alcohol[2,2]
      print uruguay_other_1986
      print third_country
      
      0.5
      Cte d'Ivoire
    复制代码
  • 索引切片

    vector = numpy.array([5, 10, 15, 20])
      print(vector[0:3])  
      [ 5 10 15]
    复制代码
  • 取某一列(:表示所有行)

    matrix = numpy.array([
                          [5, 10, 15], 
                          [20, 25, 30],
                          [35, 40, 45]
                       ])
      print(matrix[:,1])
      
      [10 25 40]
    
      matrix = numpy.array([
                      [5, 10, 15], 
                      [20, 25, 30],
                      [35, 40, 45]
                   ])
      print(matrix[:,0:2])
      
      [[ 5 10]
       [20 25]
       [35 40]]
       
      matrix = numpy.array([
                  [5, 10, 15], 
                  [20, 25, 30],
                  [35, 40, 45]
               ])
      print(matrix[1:3,0:2])
      
      [[20 25]
      [35 40]]
    复制代码
  • 对Array操作表示对内部所有元素进行操作

    import numpy
      #it will compare the second value to each element in the vector
      # If the values are equal, the Python interpreter returns True; otherwise, it returns False
      vector = numpy.array([5, 10, 15, 20])
      vector == 10
      
      array([False,  True, False, False], dtype=bool)
      
      matrix = numpy.array([
                  [5, 10, 15], 
                  [20, 25, 30],
                  [35, 40, 45]
               ])
      matrix == 25
      
      array([[False, False, False],
     [False,  True, False],
     [False, False, False]], dtype=bool)
    复制代码
  • 布尔值当索引([False True False False])

    vector = numpy.array([5, 10, 15, 20])
      equal_to_ten = (vector == 10)
      print equal_to_ten
      print(vector[equal_to_ten])
      
      [False  True False False]
      [10]
    
    
      #矩阵表示索引
      matrix = numpy.array([
                      [5, 10, 15], 
                      [20, 25, 30],
                      [35, 40, 45]
                   ])
      second_column_25 = (matrix[:,1] == 25)
      print second_column_25
      print(matrix[second_column_25, :])
      
      [False  True False]
      [[20 25 30]]
    复制代码
  • 对数组进行与运算

    #We can also perform comparisons with multiple conditions
      vector = numpy.array([5, 10, 15, 20])
      equal_to_ten_and_five = (vector == 10) & (vector == 5)
      print equal_to_ten_and_five
      
      [False False False False]
      
      
      vector = numpy.array([5, 10, 15, 20])
      equal_to_ten_or_five = (vector == 10) | (vector == 5)
      print equal_to_ten_or_five
      
      [ True  True False False]
    复制代码
  • 值类型转换

    vector = numpy.array(["1", "2", "3"])
      print vector.dtype
      print vector
      vector = vector.astype(float)
      print vector.dtype
      print vector
      
      |S1
      ['1' '2' '3']
      float64
      [ 1.  2.  3.]
    复制代码
  • 聚合求解

    vector = numpy.array([5, 10, 15, 20])
      vector.sum()
    复制代码
  • 按行维度(axis=1)

    matrix = numpy.array([
                     [5, 10, 15], 
                     [20, 25, 30],
                     [35, 40, 45]
                  ])
     matrix.sum(axis=1)
     array([ 30,  75, 120])
    复制代码
  • 按列求和(axis=0)

    matrix = numpy.array([
                      [5, 10, 15], 
                      [20, 25, 30],
                      [35, 40, 45]
                   ])
      matrix.sum(axis=0)  
    复制代码
  • 矩阵操作np.arange生成0-N的整数

    import numpy as np
      a = np.arange(15).reshape(3, 5)
      a
    
      array([[ 0,  1,  2,  3,  4],
             [ 5,  6,  7,  8,  9],
             [10, 11, 12, 13, 14]])
             
      a.ndim
      2
      
      a.dtype.name
      'int32'
      
      a.size
      15
    复制代码
  • 矩阵初始化

    np.zeros ((3,4)) 
      
      array([[ 0.,  0.,  0.,  0.],
     [ 0.,  0.,  0.,  0.],
     [ 0.,  0.,  0.,  0.]])
     
    
      np.ones( (2,3,4), dtype=np.int32 )
      
      array([[[1, 1, 1, 1],
      [1, 1, 1, 1],
      [1, 1, 1, 1]],
    
     [[1, 1, 1, 1],
      [1, 1, 1, 1],
      [1, 1, 1, 1]]])
    复制代码
  • 按照间隔生成数据

    np.arange( 10, 30, 5 )
      array([10, 15, 20, 25])
    
      np.arange( 0, 2, 0.3 )
      array([ 0. ,  0.3,  0.6,  0.9,  1.2,  1.5,  1.8])
    复制代码
  • 随机生成数据

    np.random.random((2,3))
      
      array([[ 0.40130659,  0.45452825,  0.79776512],
     [ 0.63220592,  0.74591134,  0.64130737]])
    复制代码
  • linspace在0到2pi之间取100个数

    from numpy import pi
      np.linspace( 0, 2*pi, 100 )
    
      array([ 0.    ,  0.06346652,  0.12693304,  0.19039955,  0.25386607,
          0.31733259,  0.38079911,  0.44426563,  0.50773215,  0.57119866,
          0.63466518,  0.6981317 ,  0.76159822,  0.82506474,  0.88853126,
          0.95199777,  1.01546429,  1.07893081,  1.14239733,  1.20586385,
          1.26933037,  1.33279688,  1.3962634 ,  1.45972992,  1.52319644,
          1.58666296,  1.65012947,  1.71359599,  1.77706251,  1.84052903,
          1.90399555,  1.96746207,  2.03092858,  2.0943951 ,  2.15786162,
          2.22132814,  2.28479466,  2.34826118,  2.41172769,  2.47519421,
          2.53866073,  2.60212725,  2.66559377,  2.72906028,  2.7925268 ,
          2.85599332,  2.91945984,  2.98292636,  3.04639288,  3.10985939,
          3.17332591,  3.23679243,  3.30025895,  3.36372547,  3.42719199,
          3.4906585 ,  3.55412502,  3.61759154,  3.68105806,  3.74452458,
          3.8079911 ,  3.87145761,  3.93492413,  3.99839065,  4.06185717,
          4.12532369,  4.1887902 ,  4.25225672,  4.31572324,  4.37918976,
          4.44265628,  4.5061228 ,  4.56958931,  4.63305583,  4.69652235,
          4.75998887,  4.82345539,  4.88692191,  4.95038842,  5.01385494,
          5.07732146,  5.14078798,  5.2042545 ,  5.26772102,  5.33118753,
          5.39465405,  5.45812057,  5.52158709,  5.58505361,  5.64852012,
          5.71198664,  5.77545316,  5.83891968,  5.9023862 ,  5.96585272,
          6.02931923,  6.09278575,  6.15625227,  6.21971879,  6.28318531])
    复制代码
  • 矩阵基本操作

    #the product operator * operates elementwise in NumPy arrays
      a = np.array( [20,30,40,50] )
      b = np.arange( 4 )
      print (a)
      print (b)
      #b
      c = a-b
      print (c)
      b**2
      print (b**2)
      print (a<35)
      
      [20 30 40 50]
      [0 1 2 3]
      [20 29 38 47]
      [ True  True False False]
    复制代码
  • 矩阵相乘

    #The matrix product can be performed using the dot function or method
      A = np.array([[1,1],
                     [0,1]] )
      B = np.array([[2,0],
                     [3,4]])
      print (A)
      print (B)
      print (A*B)
      
      print (A.dot(B))
      print (np.dot(A, B) )
      
      [[1 1]
       [0 1]]
       
      [[2 0]
       [3 4]]
       
      [[2 0]
       [0 4]]
       
      [[5 4]
       [3 4]]
       
      [[5 4]
       [3 4]]
    复制代码
  • 矩阵操作floor向下取整

    import numpy as np
      B = np.arange(3)
      print (B)
      #print np.exp(B)
      print (np.sqrt(B))
      
      [0 1 2]
      [0.         1.         1.41421356]
      
      #Return the floor of the input
      a = np.floor(10*np.random.random((3,4)))
      #print a
      
      #Return the floor of the input
      a = np.floor(10*np.random.random((3,4)))
      print (a)
      
      print(a.reshape(2,-1))
      
      [[0. 4. 2. 2.]
       [8. 1. 5. 7.]
       [0. 9. 7. 4.]]
       
      [[0. 4. 2. 2. 8. 1.]
       [5. 7. 0. 9. 7. 4.]]
    复制代码
  • hstack矩阵拼接

    a = np.floor(10*np.random.random((2,2)))
      b = np.floor(10*np.random.random((2,2)))
      print a
      print '---'
      print b
      print '---'
      print np.hstack((a,b))
      
      [[ 5.  6.]
       [ 1.  5.]]
      ---
      [[ 8.  6.]
       [ 9.  0.]]
      ---
      [[ 5.  6.  8.  6.]
       [ 1.  5.  9.  0.]]
    
      a = np.floor(10*np.random.random((2,2)))
      b = np.floor(10*np.random.random((2,2)))
      print (a)
      print ('---')
      print (b)
      print ('---')
      #print np.hstack((a,b))
      np.vstack((a,b))
      
      [[7. 7.]
       [2. 6.]]
      ---
      [[0. 6.]
       [0. 3.]]
      ---
     array([[1., 0.],
     [3., 6.],
     [4., 2.],
     [8., 7.]])
    
      a = np.floor(10*np.random.random((2,12)))
      print (a)
      print (np.hsplit(a,3))
      
      [[6. 5. 2. 4. 2. 4. 9. 4. 4. 6. 8. 9.]
       [8. 4. 0. 2. 6. 5. 2. 5. 0. 4. 1. 6.]]
      [array([[6., 5., 2., 4.],
             [8., 4., 0., 2.]]), array([[2., 4., 9., 4.],
             [6., 5., 2., 5.]]), array([[4., 6., 8., 9.],
             [0., 4., 1., 6.]])]
    复制代码
  • 任意选择切分位置

    print ( np.hsplit(a,(3,4)))   # Split a after the third and the fourth column
      
      [[2. 8. 4.    7.    6. 6. 5. 8. 8. 3. 0. 1.]
       [3. 5. 9.    4.    5. 8. 7. 6. 2. 3. 8. 4.]]
      
      [array([[2., 8., 4.],
      [3., 5., 9.]]), array([[7.],
      [4.]]), array([[6., 6., 5., 8., 8., 3., 0., 1.],
      [5., 8., 7., 6., 2., 3., 8., 4.]])]
    复制代码
  • 变量赋值

    Python基础算法库Numpy及可视化库使用实践-大数据ML样本集案例实战
  • 变量视图

Python基础算法库Numpy及可视化库使用实践-大数据ML样本集案例实战
  • copy实现变量之间没有关系

    d = a.copy() 
      d is a
      d[0,0] = 9999
      print d 
      print a
    
      [[9999    1    2    3]
       [1234    5    6    7]
       [   8    9   10   11]]
      [[   0    1    2    3]
       [1234    5    6    7]
       [   8    9   10   11]]
    复制代码
  • 寻找列最大值索引

Python基础算法库Numpy及可视化库使用实践-大数据ML样本集案例实战

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